In various storage systems, reading the data stored in a non-volatile memory involves decoding the data using soft reliability measures of respective storage values that represent the data. Decoding methods that utilize soft information are known in the art. For example, U.S. Patent Application Publication 2014/0040704, whose disclosure is incorporated herein by reference, describes an SSD controller reading from flash memory. Subsequent to failure of an initial soft-decision decoding attempt based on a nominal Log-Likelihood Ratio (LLR), soft-decision re-decoding attempts are made using compensated LLR soft-decision information sets. The compensated LLRs are pre-calculated at respective read-equilibrium points corresponding to mean shifts and variance change in the actual charge-state distributions of the flash memory channel. According to an embodiment, the attempts of soft-decision re-decoding are performed without a retry read, or alternatively overlapped with one or more retry reads.
As another example, U.S. Patent Application Publication 2013/0007559, whose disclosure is incorporated herein by reference, describes techniques for decoding storage levels in a non-volatile memory. A storage level of a cell in a multi-bit non-volatile memory is read. A minimum of Log-Likelihood Ratio (LLR) and a modified LLR to decode the storage level, wherein the modified LLR is a function of a misplacement probability is used. A value corresponding to the decoded level is written to a volatile memory.
As yet another example, U.S. Patent Application Publication 2014/0112076, whose disclosure is incorporated herein by reference, describes a method that includes storing data in a group of analog memory cells by writing respective analog values into the memory cells in the group. After storing the data, the analog values are read from the memory cells in the group one or more times using one or more respective read thresholds so as to produce readout results. Reliability measures are computed for the read analog values based on the readout results. An offset of the one or more read thresholds from an optimal read threshold position is estimated based on the reliability measures. The reliability measures are modified to compensate for the estimated offset, and the data stored in the analog memory cells in the group is decoded using the corrected reliability measures.